High frequency power amplifiers are commonly used in communications, radar, and other radio frequency (RF) systems. It is generally desirable for such power amplifiers to have wide bandwidth and operate with high efficiency. For example, modern broadband wireless protocols, such as LTE (Long Term Evolution) and IEEE 802.11ac, often involve transmission of broadband modulated waveforms that have high peak-to-average ratios. High efficiency over a relatively wide output power range is generally desirable for such applications.
Doherty amplifiers may be well-suited for such applications. Various Doherty amplifier implementations are described in U.S. Pat. No. 6,700,444 to Pengelly, U.S. Pat. No. 6,737,922 to Pengelly et al., U.S. Pat. No. 6,791,417 to Pengelly et al., U.S. Pat. No. 7,193,473 to Pengelly et al., and “A Wideband and Compact GaN MMIC Doherty Amplifier for Microwave Link Applications” by Gustafsson et al., IEEE Transactions on Microwave Theory and Techniques, Vol. 61, No. 2 (February 2013).